Consider an OFDM-IM system with \(N\)  subcarriers and total \(m\)  information bits. These \(m\)  information bits are divided into \(g\)  subblocks, where each subblock conveys \(p\)  bits, i.e., \(m=pg\) . Also, the \(p\)  bits in each subblock are mapped to one subblock of length \(n\)  in the frequency domain, where \(n = N/g\) .
The specific mapping procedure is that only \(k\)  out of \(n\)  subcarriers in each subblock are activated, where the subcarrier activation pattern (SAP) is determined by the first \(p_1\)  bits of the \(p\)  bits. Then, the \(M\) -ary modulated symbols on the \(k\)  active subcarriers are determined by the remaining \(p_2=k \log _2M\)  bits of the \(p\)  bits, i.e., \(p = p_1 + p_2\) . Of course, the idle subcarriers have zero values in the frequency domain [1]}.
